Cutaneous malignant melanoma (CMM) is one of the most virulent forms of human cancer. If untreated, virtually all melanomas will metastasize to distant sites within the body. Surprisingly, little is known about the genes of biochemical pathways affected during the transformation of a benign melanocytic nevus into a metastatic melanoma. The reason for this is somewhat obscure, but may be due to the fact that many cytogenetic, as well as molecular, changes occur within a melanoma cell, thus making it difficult to assess what events are obligatory in the development of CMM. Recently, several independent lines of evidence have pointed towards the early involvement of a melanoma-associated tumor suppressor (MATS) gene located chromosome 9p21. The identification and characterization of this gene, as outlined in this proposal, will potentially provide one of the first real clues into the etiology of CMM. In this regard, over 25 putative exons have already been identified (using the technique of exon amplification) from a 1.5-20 Mb yeast artificial chromosome (YAC) contig of the critical region on 9p21. Though preliminary, homology searches within athe Genbank database suggest that a number of these exons may belong to a novel gene (or family of genes) that participate in gene transposition or conversion. Fusion studies performed between five reduced somatic cell hybrids containing small portions of 9p and two recipient melanoma cell lines lend biological support to the placement of the MATS gene within this same region of 9p21. Three of these hybrids appear to harbor an intact version of this gene (i.e. they exhibit growth suppressive activity), whereas the other two do not. Comparing and contrasting the DNA content of these hybrids using the exon-trapped products (as well as any additional markers or clones located within the critical region) will potentially further narrow the candidate region and hasten the cloning of the MATS gene. Once the entire MATS gene has been isolated and sequenced, then its relationship in regards to ultraviolet radiation (UVR) and low melanin content in the skin (two additional risk factors for melanoma) will be ascertained. These studies will include; (i) searching for characteristics UVR mutation within the MATS gene, (ii) determining if UVR exposure alters the expression of this gene or, alternatively, if MATS deficient cells are less able to repair UV-induced DNA damage, (iii) developing a mouse model system that can ultimately by used to study the in vivo interactions of all three risk factors for melanoma (e.g. MATS gene mutations, UVR, and melanin content in the skin), and, lastly, (iv) initiating therapeutic trials on the aforementioned mice to determine the potential benefits of certain topical agents (or the MATS gene itself) in the treatment and prevention of melanoma. Overall, the studies proposed here will result in a better understanding of the genetic and environmental insults that contribute to the development of CMM, as well as potentially shed some light on the mechanism of gene conversion in humans.